Reflector for radar navigation



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REFLECTOR FOR RADAR NAVIGATION Filed Oct. 28, 1947 0 25W if ATTO YPatented May 30, 1950 REFLECTOR FOR RADAR NAVIGATION Harley Iams,Venice, Calm, assignor to Radio Corporation of America, a corporation ofDelaware Application October 28, 1947, Serial No. 782,522

7 Claims. 1

This invention relates to reflectors for radiant energy such as one typeof said reflector, comprising a spherical lens surrounded by anequatorial band of reflecting material as described in copendingapplication Serial No. 777,355 flled October 1, 1947 by Harley lame andentitled Radio reflectors. Said reflectors have the disadvantage ofexcessive weight for some applications, owing to the fact that thesphere is completely filled with dielectric material.

It is the principal object of the present invention to provide animproved type of omnidirectional reflector wherein dielectric materialis not required. The invention will be described with reference to theaccompanying drawing, wherein Figure 1 is a view in elevation of areflector in accordance with the present invention and Figure 2 is avertical section of the structure shown in Figure 1. Similar referencecharacters are applied to similar elements throughout the drawing.

The device in Figure 1 comprises generally two parts: a spherical shellI and a cylindrical or disc-shaped reflector member 3 disposedconcentrically within said shell. Shell I is made up of a large numberof wire or rod like conductors 5 lying in a somewhat spiral'formationand tilted substantially 45 degrees from the vertical at the equator tothe sphere. Thus as viewed by an observer from the axis, the conductors5 would all appear inclined in the same sense at 45 degrees with thevertical. The conductors 5 are separated by a maximum distance of notmore and preferably considerably less than wave length of the energy tobe reflected. The vertical dimension of the reflector member 3 is notsubstantially less than /2 wave length.

Referring to Figure 2 the spherical shell may be supported by arms 1extending radially from the member 3 which is in turn supported on avertical rod 9. In order to maintain an assembly in the proper positionwith reference to the horizontal plane, the connection between the rod 9and the disc 3 includes a ball and socket joint II, and a ring shapedweight I3 i secured to the bottom of the shell I. The lower endof therod 9 extends to a supporting member I5 which may be, for example theupper surface of a floating buoy. The radius of curvature of thecylindrical member 3 is approximately /2 that of the sphereis verticallypolarized. Energy striking the surface i at the point I! is partlyreflected and partly transmitted. The reflected energy goes outsubstantially in all directions and is not particularly directed towardthe source. The transmitted energy is necessarily polarized in a planeperpendicular to the wires in the vicinity of the point l1 which are 45degrees to the right. This energy strikes the inner. surface of thesphere at the point H, where the conductors I lie at an angle of 45degrees to the left looking in the direction of energy flow. Thus theinner surface at the point l9 acts as a substantially perfect concavespherical reflector, and directs the ray to a point 2| on thecylindrical reflector 3. A second reflection occurs at the point 2|,directing the ray to a point 23 on the inner surface of the sphere I.Here a third reflection occurs, causing the energy to travel along apath 25 parallel 20 to that of the incident ray. The polarization of l.Thus the cylindrical member is placed substantially at the conjugatefocal surface of sphere I in the interior thereof.

The operation of the described device is as follows: Assume first thatthe incident radiation the triply reflected energy is such that itpasses through the spherical surface at the point 21 substantiallywithout reflection and continues in the direction of the originalsource.

The above described sequence of reflections occurs with any otherapproximately horizontally incident rays such as the ray 29.Horizontally polarized energy is treated in substantially the samemanner, approximately A; of the incident energy being lost by theinitial reflection from the outside surface of the shell I. It will beapparent that substantially all of the energy would be diffused if itwere polarized in a plane parallel to the conductors 5 and thuscompletely reflected from the surface upon which it is initiallyincident and that the device would work with high efficiency if thepolarization were perpendicular to the wires 5; however, it is usual inradio signalling and radar practice to employ either vertical orhorizontally polarized energy.

I claim as my invention:

1. An omnidirectional reflector for returning incident radiant energyalong a path comprising a plurality of conductive wires, each inclinedat an angle of 45 degrees to the horizontal and disposed so as to definethe surface of a sphere, a body of conductive material in the form of aright circular cylinder with its axis of revolution extending verticallythrough the center of curvature of said spherical surface, saidcylindrical body having a height of at least /2 wave length of theenergy to be reflected.

2. In a reflector, a structure comprising a plurality of metallicmembers spaced by less than a half wavelength of the energy to bereflected,

said members being disposed to define a surface of revolution for acomplete revolution of the line generatrix thereof about an axis, saidsurface having at least one dimension greater than a half wavelength ofthe energy to be reflected, each said member being inclined in the samesense at an angle as viewed by an observer from said axis of 45 degreeswith a line parallel to said axis.

3. A reflector comprising a plurality of metallic members spaced by lessthan a half wavelength of the energy to be reflected, said members beingdisposed to define a surface of revolution for a complete revolution ofthe line generatrix thereof about an axis, said surface havingdimensions greater than a half wavelength of the energy to be reflected,each said member being inclined in the same sense at an angle as viewedby an observer from said axis of 45 degrees with a line parallel to saidaxis, and a metallic reflecting body within the defined surface andspaced from said members.

4. The reflector claimed in claim 3. said surface being a substantiallycl'osed surface.

5. The reflector claimed in claim 3, said surface being substantially acomplete sphere.

6. The reflector claimed in claim 5, said metallic body having areflecting surface in the shape REFERENCES CITED The followingreferences are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,625,946 Laird Apr. 26, 19271,830,176 Schroter Nov. 3, 1931 2,085,406 Zworykin June 29, 1937 202,130,389 Gothe Sept. 20, 1938 2,370,053 Lindenblad Feb. 20, 19452,407,318 Mieher et a1. Sept. 10, 1946 FOREIGN PATENTS 25 Number CountryDate 1 668,231 Germany May 26, 1935 770,482 France July 2, 1934

